1. Field of the Invention
This invention relates to a front suspension for a front engine front wheel drive type (FF type) vehicle, and more particularly to an improvement in a front suspension for an FF type vehicle in which the center of gravity of the body is offset from the center due to the laterally mounted engine.
2. Description of the Prior Art
In most the FF type vehicles, the engine is laterally mounted so that its output shaft extends transverse to the longitudinal axis of the body of the vehicle in order to facilitate mounting of a clutch mechanism, a differential gear, a transmission and so forth together with the engine in a limited space of the engine room. When the engine is laterally oriented, the engine is generally disposed in an off-center position toward right or left with respect to the central longitudinal axis of the body to make sufficient room for mounting those components. Since the engine is very heavy compared with the other components such as the transmission and the differential gear, the center of gravity of the body is shifted toward the side of the engine if the engine is off-center with respect to the longitudinal axis of the body.
In a vehicle whose center of gravity is not on the longitudinal axis of its body, there has been recognized a problem that the right steering effect differs from the left steering effect, which adversely affects the driving stability. That is, when turning to the side opposite to the center of gravity with a certain turning radius, the steering wheel must be rotated by a larger angle than the angle required for turning to the side of the center of gravity with the same turning radius.
Now, the reason why the difference in steering effect arises as mentioned above will be briefly described referring to FIG. 1. As is well known, there is the relation represented by the curve in FIG. 1 between the cornering power and the vertical loads placed on the wheels. When there exists the difference 2.DELTA.Fz between the loads W1 and W2 on the inner wheel and the outer wheel, the cornering power of the vehicle is equal to the average value of the cornering powers C1 and C2 of the respective wheels. As can be seen from FIG. 1, the effective cornering power of the vehicle that is the average (C1+C2)/2 of the cornering powers C1 and C2 of the inner and outer wheels is smaller than the cornering power C0 of the vehicle which would be obtained when the loads W1 and W2 on the inner and outer wheels are equal to each other and equal to the average W thereof. The difference betwen the effective cornering power (C1+C2)/2 and the cornering power C0, i.e., the reduction of the cornering power, becomes more significant as the difference 2.DELTA. Fz between the loads W1 and W2 placed on the inner and outer wheels increases.
In a vehicle whose center of gravity is not on the longitudinal axis of the body, there exists a difference between the loads on the right and left wheels even when the vehicle runs straight. However, when the vehicle turns to the side opposite to the side of the center of gravity, the load placed on the outer wheel, i.e. the wheel on the side of the center of gravity, is increased and the load placed on the inner wheel (which has borne a smaller load than on the other wheel from the first, i.e. from the static state of the vehicle) is reduced due to the centrifugal force, whereby the difference 2.DELTA.Fz between the loads W1 and W2 on the inner and outer wheels is enlarged to increase the reduction of the cornering power. On the other hand, when the vehicle turns to the side of the center of gravity, a part of the express load on the inner wheel over that on the outer wheel in the static state of the vehicle is moved to the outer wheel due to the centrifugal force and accordingly the difference 2.DELTA.Fz between the loads W1 and W2 on the inner and outer wheels is reduced to lower the reduction of the cornering power. Therefore, in a vehicle whose center of gravity is not on the longitudinal axis of the body, the steering angle .beta. by which the steering wheel is required to be rotated when turning to the side opposite to the side of the center of gravity with a certain radius is larger than the same when turning to the side of the center of gravity, and vice versa.
Further, in FF type vehicles in which the engine is laterally mounted, the transmission and the differential gear are generally disposed on the side of the engine, namely these components and the engine are arranged laterally with these components located on the longitudinal axis side of the engine. Therefore, the one of the driving shafts which extends from the differential gear to the wheel on the side of the engine must be inherently longer than the other driving shaft. When the vehicle is running, a moment inwardly turning each front wheel about the driving shaft is generated due to the driving torque. The moment exerted on the one of the front wheels connected to the shorter driving shaft which forms a cathedral angle larger than that formed by the longer driving shaft is larger than the moment exerted on the other front wheel connected to the longer driving shaft. Accordingly, the steering wheel is apt to be biased toward the wheel connected to the longer driving shaft.
In the FF type vehicle, the above two actions combine to make the steering effect to the side of the center of the gravity of the body larger than the steering effect to the opposite side.
In Japanese Unexamined Patent Publication No. 52 (1977)-22225, there is disclosed a front suspension for removing the biasing effect on the steering due to the difference of the cathedral angle by setting the degree of center-offset of the wheel connected to the longer driving shaft larger than that of the wheel connected to the shorter driving shaft. Further, in Japanese Unexamined Patent Publication No. 54(1979)-138235 and Japanese Utility Model Publication No. 49(1974)-20039, there is disclosed a front suspension in which the differential gear is inclined so that the difference in the cathedral angle between the longer driving shaft and the shorter driving shaft is minimized. However, the suspensions disclosed in the above publications cannot compensate for the difference in the steering effect or the difference between the cornering powers in turning to the right and left due to the difference between the loads on the right and left front wheels, though they are effective in preventing the biasing effect on the steering due to the difference in the cathedral angle.